A gear which has undergone gear cutting processing by a gear cutting machine such as a hobbing machine is further subjected to finishing processing by a gear finishing machine such as a gear grinding machine.
In the finishing processing of the gear, before actually starting finishing processing (grinding), a process of “meshing” for achieving rotation phase relation wherein teeth (mountains and valleys) of a grinding tool such as a screw-like grindstone can be meshed with teeth (mountains and valleys) of a work gear (for example, a gear which has undergone hob cutting and quenching) is required.
In the meshing process, the meshing angle of the work gear attached to a table shaft is required to be obtained. As a method for obtaining the meshing angle, conventionally, a method in which the positions of the teeth (mountains and valleys) of the work gear are detected by a touch probe, which is a contact type sensor, or a nearby sensor, which is a non-contact type sensor, and the meshing angle is obtained by an NC device based on detected signals thereof has been used.
For example, when the nearby sensor is used, as shown in FIG. 15, after a nearby sensor head 4, which is a detection unit of the nearby sensor, is disposed in the vicinity of teeth 3 of a work gear 2 attached to a table shaft 1, both left and right tooth surfaces 6 and 7 of the work gear 2 are detected by the nearby sensor head 4 while the work gear 2 is rotated together with the table shaft 1 as shown by an arrow A by an unshown motor, and the detection signals thereof are output to an NC device via a nearby sensor amplifier 5, which is a signal processing unit of the nearby sensor.
Note that prior art documents describing meshing of gears include the followings.    Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. 2004-25333    Patent Document 2: Japanese Patent No. 3132740    Patent Document 3: Japanese Patent Application Laid-Open (kokai) No. 2000-326141